Reciprocating, sucker rod-driven, downhole pumps are commonly used in wells to raise produced fluid to ground surface from a subsurface formation.
This type of pump usually incorporates a pair of ball and seat valves in its plunger. These valves are referred to as the standing and travelling valves.
In general, these valves comprise:                a vertically oriented, cylindrical, tubular cage forming a through-bore and having internal ball guide flanges;        a horizontal annular seat extending across the bore at its lower end——the seat is supported by the cage;        a ball positioned within the cage bore; and        a transverse ball stop extending across the upper end of the bore and connected with the cage wall;whereby the ball can seat on the seat to close the bore or may be unseated by pressure from below to permit fluid to pass upwardly a round the ball and between the guide flanges. The fluid exits through top outlets formed between the ball stop crossbars and the cage side wall.        
There have been many features incorporated into this basic combination over the years, to achieve various objectives. Three such objectives are improving durability, volumetric flow and pressure drop characteristics.
In connection with improving durability, it is known to provide the ‘cage’ in the form of an external, tubular, cylindrical ‘shell’ and an internal, slidingly received ‘insert’. The insert is formed of hard alloy. A typical prior art shell/insert assembly is shown in FIG. 1.
More particularly, the shell/insert assembly comprises:                An external steel shell, which has an internal stop shoulder for locking in the insert at the upper end and which supports and contains separate annular seat and sealed spacer members at its lower end; and        An insert which comprises horizontal top and bottom rings joined by vertical, circumferentially spaced apart ribs forming side openings or “windows” between them. The ribs support inwardly projecting ball guide flanges arching inwardly to form a semi-spherical ball stop for retaining the valve ball. The side openings provide passageways for fluid flow around the ball. The flanges and top ring further form top outlets for egress of the fluid from the upper end of the inset.        
The present invention is concerned with providing a modified insert which is designed with a view to improving volumetric flow. In addition, in a preferred embodiment the invention also seeks to incorporate desirable flow pattern and pressure drop characteristics.